Metal with phosphide case and method of producing same



July 16, 1935. R; B MCCAULEY METAL WITH PHOSPHIDE CASE AND METHOD OF PRODUCING SAME Filed Feb. 29, 1932 2 SheebS-Shee 1 aai@ July 16, 1935. A R, B. MCCAULEY 2,007,977

METAL WITH PHOSPHID CASE AND METHOD OF PRODUCING SAMEv Filed Feb. 29, 1932 2 sheets-Sheet 2 Patented July 16, 1935 UNITED sTATEs PATENT OFFICE METAL Wrr'H-'Pnosrnmn CASE AND METHOD or PRoDUcINGsAME Roy B; McCauley, Chicago Heights," Apjilieatipn February 29, 1932, smal No. 595,849 i1 claims.- (crus-A1) The object of the presentI inventionis to produce upon an article made of iron, steel and some other metals known tojreact with phosphorus to form phosphides andby'reaction upon the metal itself, a case that will render the article substantially immunexto attack fromacids, alkalies and other chemical influences.

While the principle yhas long been realized that alloying phosphorus with iron and steel increases lo the resistance ofthe metal to surface corrosion and other chemical attack, it has not to my knowledge hitherto been applied in a manner to successfully develop, upon an article of such metals, a case consisting of an alloy of phosphorus with the metal, of suzchv depthand such union with the bodyr of non-phosphorized metal as 4will t insure permanency of the case and complete exclusion of corroding inuences from the metal.

The present invention resides in asinple, eflicientand comparatively inexpensive method'of procedure whereby an existing artile of iron, steel or some other metal may, without injuring the article by excessive temperature, be. converted into a new article of manufacture by having developed upon it a phosphorus alloy case of such inherent chemical formula and inherent character; of such penetration into the body or depth of case, and with such diffusion of merger with the portion of the article that is not alloyed with phosphorus, that thecase will not be readily removed by abrasion, spalling or ilaking oll, and it will hermetically exclude from the body of the metal, corrosiveand other reacting inuences to, which phosphided metal is immune.

The invention is characterized by the condiftions, among others, that the alloying of phosphorus with the metal of the article is carried ,out in a manner to cause the protective case to g exist in the form of -a phosphide of the .metal oi the article, as distinguished from a phosphate or otheri'orm of combine., This phosphide isdeveloped at a temperature that is so far below the `critical temperature of the metal of the article ,as to exclude. any distortion of the design of the article or any injury to its metal structure. 'I'he pl'xosphidei-forming conditions are such that they may be maintained,` for any desirable period of time by way of regulating the depth to which 'the reaction penetrates and consequent thickness of' the resultant case, thus enabling the conversion VYthroughout the-affected area as to leave any ac'- curately defined plane of demarcation between the phosphide and the non-phosphorized metal, but leaves, rather,a condition that I shall herein .term` diffused merger of the thus-alloyed and 5 y non-alloyed portions, so that` spalling oi, chipping, or aking of the substantial thickness of phosphideV does not occur. The yprocedure lends itself readily tointroduction of the elementl of pressure as an infiuenceupon the reaction to such extent as may be desired. And an aqueous prolof this aqueous protection for pure phosphorus reagent may'continue throughout the process or be continued only during the time necessary' to charge the treatment chamber with the goods and reagent, with exclusion of air, or. may be omitted altogether; and in any event, vaporization of the phosphorus itselfr in the hermetic treatment chamber, by the heat of the treatment, may be relied upon to develop internal pressure desired in influencing the reaction.

yIn many instances it will bey desirable to use .30 relatively high temperatures (less thany the critical temperature ofthe metal of the article) and in 'so doing to'employ as asource of reagent, phosphorus released by reduction, under the heat of the process from one of its compounds, orstill more conveniently prepared in the form of phosphine. Generally speaking, vthe depth of Vthe protective case will be influenced bythetime during which the reaction is continued, and this circumstance renders desirable the use of a-phos- 40 phorus source, such as phosphine, which can be fed into the treatment chamber as long as may be desirable. The temperature maintained during the reaction will strongly influence the rate of the reaction. 4

In carrying out the method of the invention, and producing the new article of the invention, several procedures may be followed.

One procedure would be to enclose an article, made of iron orl steel or some other metal appropriate to the procedure, in a chamber and subject it to the action ofmolten phosphorus submerged in water heated up to 212 F.; and this may be varied to the extent of having the chamber closed tightly enough to conilne steam under substantial pressure and thereby subject the work to a temperature materially above 212 F.

According to a second procedure, the metal article may beenclosed with metallic phosphorus in a container capable of withstanding high pressure and such pressure developed by heating and vaporizing the phosphorus; the degree of pressure being dependent on the size of the chamber and the quantity of phosphorus introduced'. And in this second procedure the phosphorus may be initially protected by water until the heating chamber can be hermetlcally sealed, the water being in an open container from which it will readily disappear by evaporatIon early in the procedure leaving the phosphorus subject to vaporization, or the phosphorus may be initially Y protected by introducing it in the form of a car-- tridge or sealed in va suitable destructible envelope which would be ruptured by the pressure of the phosphorus when vaporized within it, thus releasing the phosphorus for reaction as the temperature is developed.

According to a third procedure, theV phosphorus source may be phosphide of a metal having a less amnity for phosphorus than'has the metal of whichthe article is made, the metal phosphide being packed around the article to be cased and the transfer of thephosphcrus being induced by the heat of the procedure.

A fourth procedure embodying the method of the invention and producing the new article of manufacture, and one which is preferred because of the great flexibility which it offers in temperature and pressure of the reacting environment, as well as facility for continuing the supply of the reagent. and thereby controlling the time during which the reaction is continued,

,consists in placingthe article to be cased in a chamber, for instance, a tube, one end of which has a venting tube submerged in water to a depth that will impose a desired back pressure within the chamber, and the other end of which said chamber is in. communication with a container or generator of phosphine (PHa): the said tubular chamber being located within a heater capable of developing a desired temperature in the chamber. In this fourth procedure, the reaction can be regulated by not only the temperature maintained, but largely, and particularly as to rapidity, by controlling the input of the phosphine. Through means of this fourth procedure involving the method of the invention, and with a reaction of phosphine through a period of about one half an hour, upon an article made of steel I have produced a case havingI a depth of one sixty-fourth (1/64th) of an inch and consisting of an iron phosphide corresponding to the formula Fea P (which is 15.63% phosphorus), and have tested such article with its said case by immersing it in a 10% solution of hydrochloric acidfor a period of thirty days and found that the article didnot lose appreciably in weight, and its case was firmly secure against chipping off.

Also, by the above described fourth procedure or embodiment of the method of the invention, I have treated articles made of steel having a carbon content in one instance of three onehundredths of one per cent (.03%), and in another instance one per cent (1.00%) and, by such treatment lasting over a period of about four hours and using phosphine as the reagent, formed upon said articles phosphide cases having a depth of about one thirty-second (1/32nd) of an inch, corresponding to the formula Fez Ps, which is 45.45% phosphorus. In one of these latter experiments, a piece of one per cent (1.00%) carbon steel, in developing its phosphide case of Fe: P: formula (45.45% phosphorus), was l of hydrogen which, in turn, reacted with the iron oxide scale and left the latter upon the specimen in the form of iron according to the formulas 2PK: plus 4Fe yields ZFezP plus 3Hz, and 3H: plus FezOa yields 2Fe plus 31120; the resulting iron being then converted to iron phosphide by the incoming PH: gas as 2PK: plus 4Fe yields 2FezP plus 3Hz.

If at any time during the operation of the fourth procedure an excess of phosphine is delivered to the tubular chamber, it will be manifested by self ignition of the phosphine on reaching atmosphere of room temperature in escaping from the waterl into which the venting tube is dipped, and this converts it into phosphoric acid (P205) by the reaction of 2PH3 plus 402 yields P205 plus 3Hz0.' If the bubbles coming through the water into which the venting tube is dipped do not take fire on reaching atmosphere, it may safely be assumed that the atmosphere in the sreaction chamber is hydrogen and the phosphine entering the chamber is not excessive.

In the accompanying drawings, four suggestive designs of apparatus convenient for practicing the invention are shown by way of illustration- Figure 1 showing, in side elevation, a small installation for casing small articles;

Figure 2 showing, partly in side elevation and partly in longitudinal section, an installation with the reaction chamber designed for treating long articles, such as pipes and tubes, enclosed in a furnace.

Figure 3 showing, partially in longitudinal section, an apparatus in which the reaction chamber is in the form of a wheeled car running on a track and employing an extraneous source of heat; and

Figure 4 showing in side elevation, partly in section, an apparatus in which an electricy resistance element is used as the source of heat.

Referring to Figure 1, I represents a commercial cylinder of phosphine gas, 2 a commercial cyllnder of inert gas such as hydrogen, 3 a threeway valve receiving gas from cylinders I or 2 and discharging the same through pipe 4 into reaction chamber 5 contained within a furnace 6, which may be equipped with usual accessories such as heat source 1, furnace door 8, pyrometer ,tube 9 and gauge I0. From the reaction chamber 5 extends a venting pipe.|I which dips into a body of water I2 a distance suiilcient to develop a desired back pressure in pipe Il and thereby regulate the pressure under which reaction in chamber 5 proceeds. This apparatus may also be provided with loading and unloading table I3.

AAfter an apparatus such as illustrated in Figure 1 is assembled for phosphorlzing, that is to say, the articles to be cased are enclosed in the reaction chamber 5, the air should be washed out of the apparatus by means of a current of hydrogen from the container 2, or it may be ordinary illuminating gas, in order to insure a reducing instead of anoxidizing atmospherev in the chamber. This being done, gas from cylinderv 2is cut off and phosphine (PHa) from cylinder l is introduced into the reaction chamber l., and while thetemperature of' the `furnace l is kept up toa degree just above that necdedfor the reaction,-say,ia temperature of from 300 to 800 F., the introduction of phosphine is-continued at la rate which will supply the reaction for a periody `lasting from one-half to five hours, according to the depth' of case desired, after which the delivery of the reagentV may be cut off, the apparatus'opened up and the goods removed. 'I'he case developed upon the goods will appear as 'a bright, silvery surface, It the temperature of 4the reaction chamber should rise to above 1400 F. which is above-the critical point of the iron or steel, not-only would the goods be subject to injury by distortion, but the phosphorized surface metal wouldV appear as a black, brittle case of iron phosphide which does not penetrate the metal, but would be liable to flake lor be easily rubbed olf. 'I'he surfacing wouldact as iron phosphide does when not alloyedY with some other element. Such a coating has been referred to as an oxy-phosphide which, in fact, is not a phosphide at all but an ox'y-salt of the metal with which the` phosphorus reacted.

During the procedure with the apparatus as described in Figure 1, the pressure maintained in the reaction chamber 5 is that produced by subl merging the end of the vent pipe Il in the body of water vI 2, and which may be regulated by changing the degree of said submergence.

In the apparatus shown in Figure 2, the re- I In Figure 3, cylinders Ib, 2b deliver gases un-` der control of valve 3b, through pipe 4b, into a reaction chamber b which is in the form of a wheeled vehicle running on track I4 into a furnace 6b which may receive heat from any suitable source typified by hot air pipe lb leading from a suitable combustion chamber. Chamber 5b is vented by pipe lib dipping into water receptacle l2b, as in thecases of Figures 1 and 2.

Figure 4 shows a form of apparatus in which the gaseous reagent vis generated in adjunctive apparatus consisting of phosphine generator Ic discharging into storage gasometer |5whence gas escapes through pipe 4c past three-Wayv valve 3c which also communicates, by way of pipe 2c, with a source of illuminating gas; said valve 3c being made to deliver through pipe 4c' into an elongated reaction-'chamber 5c enclosed in a furnace 6c heated by electric resistance element 1c. Reaction chamber 5c in this instance is vented by pipe llc dipped into water receptacle 2c, as before. 4 is substantially that used in producing the experimental cased articles referred to in this specification. The phosphine was generated in the apparatus, although it is to be noted that commercial phosphine can now be purchased in cylinders, under pressure, such, for instance, as is used in other commercial processes, so that The apparatus shown in Figure generation -of phosphine inv situ may not ordif narilybe necessary.v f y y 1 l, In the use-.of 4any-,of the apparatus disc1osed,z;at the end of the-.time neededto give the desired iron phosphide conversion on the surface 913, the g article, thelreagent gas input-is-slowed down and the temperature of the reaction` c hainber A increased .somewhat to f allowl the phosphorus to penetrate deeper into the surface. At the'end of this last-named period, the tube will `be cooled down to below the'temperature atwhich theV article would oxidize in air;` theflowof phosphine reagent is stopped altogether; Vthe apparatus-,is again washed out with hydrogen or illuminating gas; and the phosphided'or cased article or articles then removed from the reaction chamber. By the method and apparatus herein described, metal objects already fabricated or ilned with the article "under pressure materially above atmosphere and at a temperature below the critical temperature of the metal of the article but at least as highas the vaporizing point of the phosphorus, oxygen, nitrogen and other volatiles reactive as to the phosphorus being excluded.

2. The process described in claim 1, in which the conilned reaction space is initially scavenged to free it from air, and the phosphorus, during the scavenging period is protected by an enveloping medium from which it is releasable by vaporization.

3. The process described in. claim 1, in which pressure is maintained in the reaction space by confinement of the vapor of the phosphorus.

4. 'I'he process described in claim 1, in which the said phosphorus reagent is disengaged, under the heat maintained in the reaction, from a phosphide of aimetal having less aiiinity for the phosphorus than the subject metal being converted and presented, inthe form of gas, to the metal being treated.

5. The process described in claim 1,.in which the confined reaction space is primarily scavenged by the delivery thereto of hydrogen gas suicient in quantity to displace from said space, air or other oxidizing influence which precedes the free or nascent phosphorus therein.

6. uThe process described in claim 1, in which the confined reaction space is primarily scav` enged bythe delivery thereto of hydrogen gas.

sufficient in quantity to displace from said space, air or other oxidizing influence which precedes the free or nascent phosphorus therein; the introduced hydrogen gas being supplied in quan- `tity sufficient to reduce oxide scale upon the suriace of the subject metal.

7. The process described in claim 1, in which the reaction between the phosphorus and the metal is interrupted after but a portion of the subject-metal has been converted into its phosphide and thereby leaving a body of non-phosphorize'd subject metal with a phosphide case united thereto through a diffused region of merger. Y

8. The process described in claim 1, in which the reaction between the phosphorus and the metal is interrupted after but a portion of the subject metal has been converted into its phosphide; a body of non-phosphorized subject metal is left with a phosphide case united thereto through a diiused region of merger; and the' which the source of the reacting nascent phosphorus is phosphine substantially free from other reactive elements.

10. The process described 4in claim l, in which the subject metal is mainly iron, and the converted corrosion resisting portion thereof is mainly iron phosphide.

11. 'I'he process described in claim 1, in which the subject metal is mainly iron and the converted corrosion resisting portion thereof is mainly iron phosphide, and in which said process free hydrogen is introduced in quantity sufficient to reduce the scale on the iron and leave the iron subject to reaction with the phosphorus.

ROY B. McCAULEY 

